Microelectromechanical systems (“MEMS”) are used in a growing number of applications. For example, MEMS currently are implemented as gyroscopes to detect pitch angles of airplanes, and as accelerometers to selectively deploy air bags in automobiles. In simplified terms, such MEMS devices typically have a structure suspended above a substrate, and associated electronics that both senses movement of the suspended structure and delivers the sensed movement data to one or more external devices (e.g., an external computer). The external device processes the sensed data to calculate the property being measured (e.g., pitch angle or acceleration).
The suspended structures may have very smooth outer surfaces. Consequently, if the surface of a suspended structure contacts an adjacent component, the structure and component may stick together. For example, if a suspended mass contacts an adjacent actuation electrode, the mass may stick to the electrode. This phenomenon is known in the art as “stiction,” which is a significant cause of yield loss and reliability failures in a wide variety of MEMS products. This problem can be particularly acute in the Z-direction when implementing a MEMS device with silicon-on-insulator (SOI) technology. Specifically, SOI wafers typically are very smooth to ensure that they maintain a secure bond between wafers. Such smoothness, however, enhances the probability of stiction with other layers of the device if the insulator layer under a suspended microstructure is removed.